during the periods that we cover there are several ways to spot a knight.
for the early bit (roughly 11th - 12th century) - a knight will have better, more defensive armour - a full hauberk (knee length full sleeved mail shirt), and he'll generally be armed to the teeth.
as somebody who watches from the sidelines or water carries, you quickly get used to identifying people by their hosen, cos it's the only bit you can see (unles they're wearing leg armour, which is just unhelpful

)
the lessers may have armour, but usually won't be as fully covered by it. also, it's unlikely that the lower ranks would have swords, as said.
for the later periods we cover (13th & early 14th) it starts to get easier.
generally the knight will be the one with the fancy heraldic surcote (linen if down on his luck, silk if a tart

). he might be wearing his colours in other ways, like a band of twisted silk around his helmet in his colours, or a pennant (small flag).
he'll have even more armour, to the point where you can literally only identify him by his heraldry - everything else is completely covered in metal.
again - he will almost certainly be armed to the teeth, (some of our lot regularly take to the field with three or even four weapons.
oh - and if you see conquest and see someone with a mace, he's a knight.
in history knights were made exactly as they are now - either by birth or by being knighted by the monarch (though no nice sword on shoulder thing - you get whacked in the face with a gauntlet).
doesn't have to be on horse to be a knight, and usually with our lot they're at the front, cos they're the most experienced.
Some groups try to do it with a full rank system, where new members start as squires and have to work their way up to knighthood by cleaning and polishing, fetching and carrying for several years. Surprisingly, they don't tend to be groups who recruit many people...
can't think who you mean *whistles*
somebody tried to make someone in conquest a squire once - you can imagine the response

I think concise would be a good word to use...
and I have them doing the washing up & shelling peas and stuff quite regularly off the field
generally to be a knight in conquest, you have to pass the safety tests with all the weapons you'll be using (cos they're different to the lower ranks), and have saved up to buy the kit (it ain't cheap, and it has to be consistent). and it also helps if you can shout a bit...
there is a 'knight's test'*, that some do (to prove to themselves that they can). that consists of ten minutes semi contact fighting, and five minutes no holds barred full contact. through the whole thing you get a certain amount of time 'time-outs' and you're opponents are tag teaming. if you make it, you get your silk knights girdle (like a belt), and clouted in the face during a knighting ceremony.
*doesn't happen often, and by no means a requirement, or of any real meaning.
"What a lovely hat! But may I make one teensy suggestion? If it blows off, don't chase it."
Miss Piggy
RIP Edward the avatar cat.